1. Field of the Invention
The present invention relates to a video output device for adding the blank on both left and right sides or on both upper and lower sides of an input video and outputting the video having a changed aspect ratio.
2. Description of the Related Art
Conventionally, in a television broadcasting, a program is broadcast with a video having an aspect ratio of 4/3, or 16/9. Also, the video having an aspect ratio of 16/9 may include the video of Cinemascope size having an aspect ratio of 2.35/1 with the blank added on both upper and lower sides, and the video having an aspect ratio of 4/3 with the blank added on both left and right sides. On the contrary, the video having an aspect ratio of 4/3 may include the video having an aspect ratio of 16/9 with the blank added on both upper and lower sides.
The “blank” as referred to herein corresponds to a uniform video area such as an video area having single color of black or gray.
Conventionally, a so-called wide-screen television set in which the display screen has an aspect ratio of 16/9 has also been widespread. Some wide-screen television sets has video output device for adding the blank of appropriate size on both left and right sides of the video if the aspect ratio of input video is 4/3, and outputting the video having an aspect ratio of 16/9. Also, there is a video output device for outputting the video having an aspect ratio of 4/3 into a display screen having an aspect ratio of 4/3 for the television receiver in which the video (input video) having an aspect ratio of 16/9 has the blank added on both upper and lower sides to produce the video (output video) having an aspect ratio of 4/3. The video output device inputs not only a television broadcast signal but also a reproducing video signal output from another device such as a DVD unit or a video deck as the input video (with a so-called external input terminal).
Employing the video output device, it is possible to prevent the video from being distorted on the display screen by expanding the input video in the transverse or longitudinal direction when the aspect ratio of the display screen and the aspect ratio of input video are different. More specifically, it is possible to prevent the input video having an aspect ratio of 4/3 from being expanded in the transverse direction to produce the video having an aspect ratio of 16/9 in the device with the display screen having an aspect ratio of 16/9, or conversely, to prevent the input video having an aspect ratio of 16/9 from being expanded in the longitudinal direction to produce the video having an aspect ratio of 4/3 in the device with the display screen having an aspect ratio of 4/3.
In the conventional video output device, the brightness or color of the blank to be added on both left and right sides or both left and right sides of the input video was preset, and the blank having the preset brightness or color was added on both left and right sides or both upper and lower sides of the input video. In this manner, since the blank having the brightness or color that was preset irrespective of the input video (video to add the blank) was added on both left and right sides or both upper and lower sides of the input video, there was a great difference in the brightness near a boundary between the added blank and the input video, resulting in a problem that the video was distorted near this boundary. Also, when the input video had the blank added as described above, there was a problem that the blank in brightness or color different from the blank originally added to the input video was added to the input video to produce the unnatural video on the display screen.
Incidentally, in displaying the first image and the second image adjacently, a technique for adjusting the hue in the boundary portion to prevent the distortion of video in the boundary portion has already been proposed (See JP-A-2713677 and JP-A-8-211860).
However, in the above video output devices for adding the blank on both left and right sides or both upper and lower sides of the input video and outputting the video (output video) having a changed aspect ratio, there was no video output device for preventing a distortion of video from occurring near the boundary between the input video and the added blank, or prevent an unnatural video with the blank in brightness or color that is different from the blank originally added to the input video from being displayed.